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Ultrastructural features and morphometric evaluations of water buffalo seminiferous epithelium are reported for the 6 phases of the spermatogenic cycle. The relative Sertoli cell volume varies between 30% (phase 4) and 39% (phase 8), the calculated volume of a Sertoli cell between 71 18 pm3 and 8968 pm3 (phase 4). Smooth ER is the organelle that exhibits the most prominent changes in Sertoli cells during the spermatogenic cycle: it occupies about 6% in phase 3 and 2 1 % in phase 4. All spermatogenic cells of the same clone present cytoplasmic bridges among them. From preleptotene (about 470 pm3) to late diplotene (about 2300 pm3) the volume of a primary spermatocyte increases nearly 5-fold; their nuclear volumes increase 3.5-fold in the same period. Secondary spermatocytes are found only in phase 4 of the cycle. Due to partial cell necrosis and autolysis late maturation phase spermatids display not more than 25% of the size of early cap phase spermatids. 63% of all numerically possible germ cells disappear from the seminiferous epithelium during spermatogenesis.Particularly heavy cell loss is observed in phase 4 and involves the spermatogonial fraction as well as cells during the second meiotic division.